The present invention relates to novel assemblies of conventional corrugated plastic board sheets and molded plastic connector strips or pieces which unite and lock said sheets together to produce useful products such as containers, planters, toys, wallboard panelling,house siding, and the like.
Corrugated plastic board is a laminate of exterior sheets of plastic film and an interior corrugated sheet of plastic film, similar in structure to corrugated paper board or cardboard. Reference is made to U.S. Pat. Nos. 3,837,973 and 3,999,928 for their disclosure of suitable corrugated board of synthetic thermoplastic film and methods for producing such board.
Corrugated plastic board has many advantages over conventional corrugated paper board or cardboard due to its strength, resistance to water and other liquids, resiliency or resistance to permanent compression or collapse, inertness or resistance to rotting, staining, etc. However, corrugated plastic board also has some disadvantages due to its nature. The relative inertness and nonabsorbent nature of corrugated plastic board make it difficult to unite sheets or pieces of such board to each other by means of adhesives, as is most common with corrugated paper board. Also, the "memory" properties of the thermoplastic film components of the plastic board make it difficult to bend or fold and retain such plastic board permanently in a direction perpendicular to the length of the corrugations, as is common with the forming of corrugated paper board into cardboard boxes and other structures.
Attempts to connect panels or sheets of corrugated plastic board to each other by connector strips or pieces having frictional engagement means are unsuccessful because of the slippery nature of the surface of plastic films which enables the plastic board to pull out of engagement under the application of stress.
It is known to connect solid, unitary plastic sheets or panels to molded plastic connectors by providing thru-holes in the plastic sheet or panel, which holes receive lock ramps, detents or protrusions present on the connector to provide locking engagement. Reference is made to U.S. Pat. Nos. 3,913,774 and 4,002,261 for their disclosure of such structures, although neither patent involves the use of corrugated plastic board. The main disadvantage of the structures of these patents is the necessity for thru-holes in the sheets or panels being connected, which destroys the liquid impermeability of the sheets or panels or of the containers formed therefrom. Another disadvantage, such as of the assembly of U.S. Pat. No. 3,913,774, is the requirement of spaced, opposed lock ramp and straddling means for flexing the plastic wall member in opposite directions during assembly. The flexibility requirement, and the projection of the straddling members into the receiving slot of the connector members, limits the thickness of the wall members which can be united by such means.